Security devices are being used more and more to protect currency and other valuable documents such as passports, drivers' licenses, green cards, identity cards and the like. These security devices are also used to protect commercial products such as pharmaceuticals, cosmetics, cigarettes, liquor, electronic media, wearing apparel, toys and spare parts for automobiles and aircraft from counterfeiting. In fact, it is estimated that counterfeit articles now comprise between 5% and 7% of world trade. Holograms attached to such articles have been the traditional method to foil counterfeiters.
Color shifting pigments and colorants have been used in numerous applications, ranging from automobile paints to anti-counterfeiting inks for security documents and currency. Such pigments and colorants exhibit the property of changing color upon variation of the angle of incident light, or as the viewing angle of the observer is shifted. The primary method used to achieve such color shifting colorants is to disperse small flakes, which are typically composed of multiple layers of thin films having particular optical characteristics, throughout a medium such as paint or ink that may then be subsequently applied to the surface of an object.
U.S. Pat. No. 6,761,959 incorporated herein by reference for all purposes, to Phillips et al, assigned to JDS Uniphase Corp. discloses a security article having Chromagram™ thereon. The Chromagram™ provides both color shifting and holographic effects to the viewer. In the '959 patent an organic substrate stamped with a holographic grating or pattern is coated with a color shifting multilayer film.
U.S. Pat. No. 7,630,109 in the name of Phillips et al, assigned to JDS Uniphase Corp., incorporated herein by reference for all purposes, discloses a more complex type of Chromagram™ wherein patterning is shown. In some regions, holographic effects are shown, and in other regions only color shifting effects are visible. In Phillips '109 patent a multilayer thin film filter is disclosed an organic dielectric layer serving as a spacer layer in a Fabry-Perot structure. The dielectric has embossed regions of varying thicknesses wherein the thickness within a region is substantially uniform. Each different region of a different thickness produces a different color shift. The size of one of the embossed adjacent regions is such that the color of said one region is uniform and cannot be seen by a human eye as different in color from the uniform color of an adjacent region thereto, and wherein the color within a region can be seen with magnification of at least 10:1. Phillips' teaches a Fabry-Perot device with a variable thickness dielectric layer by embossing the dielectric material to various thicknesses. Since the dielectric in regions a, b, and c as shown in FIG. 1 of the '109 patent are purposefully embossed with different thicknesses, light reflecting back to the viewer after impinging upon the reflector will be three different distinct colors. However due to the small size of the regions a, b, and c, the eye will tend to integrate and if the pixel or region defined by (a) through (d) inclusive can be seen; only a single color will be perceived. With sufficient magnification, the individual regions (a), (b), and (c) will be seen and different colors will be perceived.
Another United States patent application which discloses diffraction gratings with color shifting coatings but deviates from the teaching of Phillips et al, is U.S. Pat. No. 7,054,042, incorporated herein by reference, in the name of Holmes et al. U.S. patent '042 appears to deviate from the teaching of Phillips in that a decoupling layer is taught as way in which to separate the diffraction grating effects from the color shifting effects. Holmes suggests placing a decoupling layer between the relief structure and the thin film reflection filter, which is described to be a thin film reflection filter.
In all of these aforementioned security structures, conventional application of the coating is suggested, for example by vacuum deposition to yield conforming layers. The prior art teaches first stamping a substrate, and subsequently applying the coating layers required to create the desired patterns of reflective and color shifting coatings.
This invention deviates from the prior art teaching by using conforming coatings with non-conforming coatings on substrates having structures thereon. In preferred embodiments the structures stamped or formed upon the substrate layer are so small, for their effects to be seen, magnification is required, however in other less preferred embodiments the structures may be large enough that they can be seen without magnification when coated. By way of example logos and other readable discernible indicia are provided on these substrates and are highlighted by providing thin film coatings that contrast particular regions.
This invention provides a thin film structure that is coated on a substrate wherein the dielectric spacer layer has a varying thickness. The provision of a dielectric layer with a varying thickness has been disclosed not only by Phillips in U.S. Pat. No. 7,630,109 but also much earlier in U.S. Pat. No. 5,877,895 incorporated herein by reference for all purposes, issued in the name of Shaw et al. Mar. 2, 1999. Shaw et al disclose applying heat variably to create a dielectric layer of varying thickness.
In contrast to the prior art which uses a stamped substrate as a spacer layer coated on one side with a reflector and on another side with an absorbing layer, an embodiment of this invention uses non-conforming dielectric layer coated on a same side of a microstructured substrate as a reflective layer and absorbing layer. Therefore the Fabry-Perot structure is supported by the substrate. This provides numerous advantages. One advantage is that the coating can be removed from the substrate if coated with a release layer. Furthermore this coating can be made into shaped flakes if carefully removed from the substrate.
The Fabry-Perot structure of this invention provides different color shifting regions adjacent to one another which |preferably differ in their color from one another by at least a delta E value of 10.
It is an object of this invention to provide a device, which exhibits different color shifting regions, visible with magnification, wherein adjacent color shifting regions provide a color shift between two distinct different colors due to the dielectric spacer layer having a varying thickness.
It is an object of this invention to provide a substrate having relief structures across its surface so that a cross section thereof has a varying thickness, and to mirror that varying thickness by applying a non-conforming layer filling depressions, valleys and troughs with a dielectric material so as to provide a Fabry-Perot structure having a spacer layer which provides color shift differences corresponding to the thickness of the substrate.
It is an object of this invention to provide at least one conforming layer and a non-conforming layer to fabricate a Fabry-Perot color-shifting filter, and wherein a substrate supporting the Fabry-Perot filter is purposefully embossed with a predetermined pattern to provide encoding that will form color-shifting indicia within the filter.
It is a further object of this invention to provide a flake having a non-conforming dielectric layer with at least one conforming layer and another conforming or non-conforming layer, wherein the flake is a color shifting device.